The performance, durability and reliability of the engines and chassis of snowmobiles have recently been remarkably improved. These improvements have given rise to requirements for better running comfort and stability.
In order to meet these requirements, in place of the leaf spring type steering ski suspension system that has been widely employed, there has been proposed the use of the so called strut type steering ski suspension system. This system is suitable for increasing the upward and downward movable range (cushion stroke) of the steering ski. The strut-type steering ski suspension system is equipped with a stationary cylinder fixed to a frame, a movable cylinder slidably fitted in the stationary cylinder, and a steering ski attached to the lower end portion of the movable cylinder. The movable cylinder is biased to return downward.
The drivability and stability of a snowmobile having a right and left steering ski can be improved by widening the spacing (tread) between the steering skis. If, however, the aforementioned strut type steering ski suspension system is adapted to increase the cushion stroke, the suspension system will be vertically elongated so much that it will protrude from the chassis. The chassis is formed in a generally rounded configuration at the engine cowl. This results in a disadvantage that the tread must be narrowed thereby to sacrifice the drivability and stability, or that the tread must be widened thereby to sacrifice the design acceptability of the engine cowl.
In a strut-type suspension system according to the prior art, when a compression coil spring is used, the compression coil spring is mounted between the upper end of the movable cylinder and the frame side so that it might not be rendered inoperative by the snow frozen thereat. It has therefore been necessary to retain at an upper portion of the suspension system the length of the compression coil spring under compression, i.e., the length corresponding to that when it is compressed with its turns contacting ("compressed length"). Since this length becomes larger as the cushion stroke is increased, it has been difficult to reduce the vertical length of the suspension system as a whole while leaving the cushion stroke long as it is.
The present invention has been conceived in view of these circumstances, and contemplates to provide a steering ski suspension system for snowmobiles which has its vertical length minimized while still making it possible to provide a sufficiently large cushion stroke.